The present invention relates to a circular knitting machine for manufacturing socks, stockings and the like, with device for producing patterns with toweling stitches.
As is known, circular knitting machines for manufacturing socks and stockings or the like comprise a needle cylinder which is arranged vertically and on whose skirt a plurality of axial grooves is defined; each groove accommodates a needle in such a manner that it can slide parallel to the axis of the needle cylinder, and each needle is provided with a heel which protrudes radially from the related axial groove.
Needle actuation cams are arranged around the skirt of the needle cylinder and define paths which can be engaged by the heel of the needles when the needle cylinder is rotatably actuated about its axis with respect to the needle actuation cams. The paths defined by the actuation cams are shaped so as to cause, during the rotation of the needle cylinder about its own axis, a movement of the needles along the related axial grooves of the needle cylinder which causes the tip of the needles to protrude upward from the upper end of the needle cylinder so as to engage the thread or threads fed at a feed, or drop, of the machine and so as to subsequently retract into the needle cylinder, forming new loops of knitting linked to the previously formed loops which are cast off the needles and descend into the needle cylinder. The needle actuation cams also define paths which avoid this movement of the needles, keeping them inside the grooves of the needle cylinder so as to prevent them from taking up the thread provided at a feed, excluding them from the knitting in progress.
The actuation or exclusion of the needles at a feed of the thread or threads is obtained by means of selection devices which move the needles along the related axial grooves of the needle cylinder, so as to shift the heel of the needles from one path to another path, both of which are defined by the needle actuation cams.
Some of the selection devices currently in use comprise a selector arranged in each axial groove of the needle cylinder below the needle and provided with a heel which extends radially with respect to the needle cylinder. Each selector can oscillate in a plane which is radial with respect to the needle cylinder to pass from an inactive position, whereat it is sunk so that its heel is inside the related groove of the needle cylinder, to an active position, whereat said heel protrudes radially from the related axial groove to engage selector actuation cams which, similarly to the needle actuation cams, are arranged around the needle cylinder and have ascending portions and descending portions to move the selectors along the related axial grooves in a direction which is parallel to the axis of the needle cylinder during the rotation of the needle cylinder with respect to the actuation cams.
The selectors are shifted from the inactive position to the active position, or vice versa, by means of various types of devices which laterally face the needle cylinder and interfere, or do not interfere, depending on the actuation imparted to them, with lugs of the selectors which have been moved beforehand into the active position to return the selectors to the inactive position or to keep them in said active position and thus produce their engagement with the selector actuation cams.
Proximate to the upper end of the needle cylinder there is also a sinker ring in which a plurality of radial grooves is defined; said grooves are angularly offset with respect to the axial grooves of the needle cylinder, and each one slidably accommodates a casting-off sinker along a direction which is radial with respect to the needle cylinder. The casting-off sinkers are provided with a heel which protrudes upwardly from the radial grooves of the sinker ring and engages within a path, defined by sinker actuation cams, which causes a cyclic movement of the sinkers toward or away from the axis of the needle cylinder. With this movement, the sinkers are moved so that one of their longitudinal ends, which is flat, is arranged between two contiguous needles so that the thread, or threads, engaged by the needles rests on this portion while the needles retract into the grooves of the needle cylinder, forming new loops of knitting.
Special sinkers are used to form toweling or loop pile stitches; they have two flat portions which are mutually spaced in a direction which is parallel to the axis of the needle cylinder, are termed casting-off surfaces and are mutually separated by a tab. Said sinkers are moved in the direction of the needle cylinder axis when the contiguous needles have started their downward movement after engaging at least two threads at a feed so that the tab of the sinker is inserted between these two threads, making one thread rest on a casting-off surface and the other thread rest on the other casting-off surface, with the consequent forming of toweling stitches.
With current knitting machines it is possible to produce knitting formed completely with toweling stitches or knitting with portions with toweling stitches alternated with portions knitted with normal stitches. In this latter case, long-heeled sinkers and short-heeled sinkers are arranged in the sinker ring, for actuating the two types of sinkers in different manners so as to alternate plain knitting with toweling-stitch knitting.
In any case, with current machines it is not possible to individually actuate the casting-off sinkers so that they form toweling stitches while performing one row of knitting and form normal stitches while performing a subsequent row, so as to obtain patterns with toweling stitches alternated with normal stitches and even with a complicated outline.
On the other hand, it is not possible to individually select the sinkers by means of a selection device which faces the sinker ring in an upward position due to the bulk problems which are particularly felt in this region of the machine.